A French prosecutor’s evidence that a co-pilot deliberately flew the Germanwings Airbus A320 into terrain brings to the fore questions of whether crash-proofing technologies, many developed after the 9/11 terrorist attacks and for the unmanned aircraft industry, could be a solution for the future.

There have been at least four other crashes since 1994 that investigators believe can most likely be explained by deliberate pilot action—a Royal Air Maroc ATR 42 in 1994, a Silk Air Boeing 737 in 1997, an Egyptair Boeing 767 in 1999 and a Linhas Aereas de Mocambique (LAM) Embraer 190 in November 2013, eerily similar in details to the Germanwings crash. Deliberate action by pilots is also still pursued as one of the theories surrounding the disappearance last year of Malaysia Airlines MH370.

According to data from Flightradar24, a crowd-sourced provider of automatic dependent surveillance broadcast (ADS-B) tracking, the Germanwings co-pilot likely changed the altitude command for the Airbus’s autopilot system shortly after arriving at cruise altitude. After the captain left the cockpit, the co-pilot presumably dialed the autopilot system hold altitude down to 100 ft. Flightradar24 officials say it took two days to decode the ADS-B data, which is included in the transponder stream and had been sent to investigators in addition to being published online.

The autopilot appears to have followed the command, descending the aircraft to the set altitude—well below the terrain in the area. There were no automated reports of equipment failures.

Similar circumstances surrounded the LAM crash in Africa. A preliminary report from Namibia’s aircraft accident investigation team on the LAM E190 crash, issued in late 2013, revealed that the captain was alone on the flight deck in cruise at flight level 380 (about 38,000 ft.)—the same altitude of the Germanwings’ A320 before its unannounced descent—when the flight data recorder showed that the altitude command for the autopilot system was manually changed to an altitude below the terrain. The first officer had left the flight deck to use the lavatory; the aircraft’s mechanical health was not in question.

The aircraft descended at high rates on a relatively constant heading, with the captain changing throttle settings and deploying speed brakes, most likely to keep the aircraft from exceeding its maximum dive velocity. This scenario was replicated in an E190 simulator owned by Azul and shown to be “very close” to the data recorder output. As with Germanwings evidence provided by prosecutors, the cockpit voice recorder in the LAM crash revealed sounds of “repeated banging” on the cockpit door, presumably by the first officer attempting to reenter the flight deck. The final report is pending.

While cockpit procedures (such as requiring at least two crew members on station at all times) and pilot psychological evaluations will likely take on heightened importance in the wake of the Germanwings crash, so too will technological solutions that could prevent deliberate actions by a crew or commandeer. 

Work underway at NASA into single-pilot operations opens the door for a system that would permit a ground-based first officer to take control of the aircraft; however, the current form of the research would allow that only if the captain onboard allowed the takeover. A senior aerospace executive familiar with the work says the single-pilot technology exists, but the larger question is whether the next step will be to go from two pilots onboard to zero. He says a lone pilot would have no colleague that could stop him or her if they wanted to do harm to the aircraft, either as part of a terrorist plot or simply a mental breakdown.

Other work conducted post-9/11 could take on new relevance. Honeywell developed an automatic recovery system for fly-by-wire aircraft, proving the concept in a Beechcraft King Air and United Airlines A319 in 2005. Rather than providing a pilot with an audio or visual warning, as is the case with terrain awareness and warning systems, the new system would automatically take control of the aircraft to avoid obstacles—at the time these were presumed to be buildings with high political value.